The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the spine. The present invention is particularly suited for the treatment of herniated discs.
The major causes of persistent, often disabling, back pain are disruption of the disc annulus, chronic inflammation of the disc (e.g., herniation), or relative instability of the vertebral bodies surrounding a given disc, such as the instability that often occurs due to a degenerative disease. Intervertebral discs mainly function to cushion and tether the vertebrae, providing flexibility and stability to the patient""s spine. Spinal discs comprise a central hydrostatic cushion, the nucleus pulposus, surrounded by a multi-layered fibrous ligament, the annulus fibrosis. As discs degenerate, they lose their water content and height, bringing the adjoining vertebrae closer together. This results in a weakening of the shock absorption properties of the disc and a narrowing of the nerve openings in the sides of the spine which may pinch these nerves. This disc degeneration can eventually cause back and leg pain. Weakness in the annulus from degenerative discs or disc injury can allow fragments of nucleus pulposis from within the disc space to migrate into the spinal canal. There, displaced nucleus or protrusion of annulus fibrosis, e.g., herniation, may impinge on spinal nerves. The mere proximity of the nucleus pulposis or a damaged annulus to a nerve can cause direct pressure against the nerve, resulting in numbness and weakness of leg muscles.
Often, inflammation from disc herniation can be treated successfully by non-surgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosteroids. In some cases, the disc tissue is irreparably damaged, thereby necessitating removal of a portion of the disc or the entire disc to eliminate the source of inflammation and pressure. In more severe cases, the adjacent vertebral bodies must be stabilized following excision of the disc material to avoid recurrence of the disabling back pain. One approach to stabilizing the vertebrae, termed spinal fusion, is to insert an interbody graft or implant into the space vacated by the degenerative disc. In this procedure, a small amount of bone may be grafted from other portions of the body, such as the hip, and packed into the implants. This allows the bone to grow through and around the implant, fusing the vertebral bodies and alleviating the pain.
Until recently, spinal discectomy and fusion procedures resulted in major operations and traumatic dissection of muscle and bone removal or bone fusion. To overcome the disadvantages of traditional traumatic spine surgery, minimally invasive spine surgery was developed. In endoscopic spinal procedures, the spinal canal is not violated and therefore epidural bleeding with ensuing scarring is minimized or completely avoided. In addition, the risk of instability from ligament and bone removal is generally lower in endoscopic procedures than with open discectomy. Further, more rapid rehabilitation facilitates faster recovery and return to work.
Minimally invasive techniques for the treatment of spinal diseases or disorders include chemonucleolysis, laser techniques and mechanical techniques. These procedures generally require the surgeon to form a passage or operating corridor from the external surface of the patient to the spinal disc(s) for passage of surgical instruments, implants and the like. Typically, the formation of this operating corridor requires the removal of soft tissue, muscle or other types of tissue depending on the procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back, etc.). This tissue is usually removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon""s view of the target site.
Once the operating corridor is established, the nerve root is retracted and a portion or all of the disc is removed with mechanical instruments, such as a pituitary rongeur. In addition to the above problems with mechanical instruments, there are serious concerns because these instruments are not precise, and it is often difficult, during the procedure, to differentiate between the target disc tissue, and other structures within the spine, such as bone, cartilage, ligaments, nerves and non-target tissue. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone within the spine, and to avoid damaging nerves, such as the spinal nerves and the dura mater surrounding the spinal cord.
Lasers were initially considered ideal for spine surgery because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, bones, ligaments and spinal nerves often lie within close proximity of the spinal disc, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.
Monopolar radiofrequency devices have been used in limited roles in spine surgery, such as to cauterize severed vessels to improve visualization. These monopolar devices, however, suffer from the disadvantage that the electric current will flow through undefined paths in the patient""s body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient""s body. In addition, since the defined path through the patient""s body has a relatively high impedance (because of the large distance or resistivity of the patient""s body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
Other disadvantages of conventional RF devices, particularly monopolar devices, is nerve stimulation and interference with nerve monitoring equipment in the operating room. In addition, these devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a xe2x80x9ccutting effectxe2x80x9d along the pathway of localized tissue heating. Thus, the tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site. This collateral tissue damage often causes indiscriminate destruction of tissue, resulting in the loss of the proper function of the tissue. In addition, the device does not remove any tissue directly, but rather depends on destroying a zone of tissue and allowing the body to eventually remove the destroyed tissue.
The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures within a patient""s body, such as tissue within or around the spine. The systems and methods of the present invention are useful for ablation, resection, aspiration, collagen shrinkage and/or hemostasis of tissue and other body structures in open and endoscopic spine surgery. In particular, the present invention includes a channeling technique in which small holes or channels are formed within intervertebraldiscs, and thermal energy is applied to the tissue surface immediately surrounding these holes or channels to cause thermal damage to the tissue surface, thereby stiffening the surrounding tissue structure and for reducing the volume of the disc to relieve pressure on the surrounding nerves.
Methods of the present invention include introducing one or more active electrode(s) into the patient""s spine and positioning the active electrode(s) adjacent the target tissue, e.g., a disc. High frequency voltage is applied between the active electrode(s) and one or more return electrode(s) to volumetrically remove or ablate at least a portion of the target tissue, and the active electrode(s) are advanced through the space left by the ablated tissue to form a channel, hole, divot or other space in the disc tissue. The active electrode(s) are then removed from the channel, and other channels or holes may be formed at suitable locations in the disc. In preferred embodiments, high frequency voltage is applied to the active electrode(s) as they are removed from the hole or channel The high frequency voltage is below the threshold for ablation of tissue to effect hemostasis of severed blood vessels within the tissue surface surrounding the hole. In addition, the high frequency voltage effects a controlled depth of thermal heating of the tissue surrounding the hole to thermally damage or create a lesion within the tissue surrounding the hole to debulk and/or stiffen the disc structure, thereby relieving neck or back pain.
In a specific configuration, electrically conductive media, such as isotonic saline or an electrically conductive gel, is delivered to the target site within the spine to substantially surround the active electrode(s) with the conductive media. The conductive media may be delivered through an instrument to the specific target site, or the entire target region may be filled with conductive media such that the electrode terminal(s) are submerged during the procedure. Alternatively, the distal end of the instrument may be dipped or otherwise applied to the conductive media prior to introduction into the patient""s body. In all of these embodiments, the electrically conductive media is applied or delivered such that it provides a current flow path between the active and return electrode(s). In other embodiments, the intracellular conductive fluid in the patient""s tissue may be used as a substitute for, or as a supplement to, the electrically conductive media that is applied or delivered to the target site. For example, in some embodiments, the instrument is dipped into conductive media to provide a sufficient amount of fluid to initiate the requisite conditions for ablation. After initiation, the conductive fluid already present in the patient""s tissue is used to sustain these conditions.
In an exemplary embodiment, the active electrode(s) are advanced into the target disc tissue in the ablation mode, where the high frequency voltage is sufficient to ablate or remove the target tissue through molecular dissociation or disintegration processes. In these embodiments, the high frequency voltage applied to the active electrode(s) is sufficient to vaporize an electrically conductive fluid (e.g., gel, saline and/or intracellular fluid) between the active electrode(s) and the tissue. Within the vaporized fluid, a ionized plasma is formed and charged particles (e.g., electrons) are accelerated towards the tissue to cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. The short range of the accelerated charged particles within the plasma layer confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 to 150 microns with minimal heating of, or damage to, surrounding or underlying tissue structures. A more complete description of this phenomena is described in commonly assigned U.S. Pat. No. 5,697,882 the complete disclosure of which is incorporated herein by reference.
The active electrode(s) are usually removed from the holes or channels in the subablation or thermal heating mode, where the high frequency voltage is below the threshold for ablation as described above, but sufficient to coagulate severed blood vessels and to effect thermal damage to at least the surface tissue surrounding the holes. In some embodiments, the active electrode(s) are immediately removed from the holes after being placed into the subablation mode. In other embodiments, the physician may desire to control the rate of removal of the active electrode(s) and/or leave the active electrode(s) in the hole for a period of time, e.g., on the order of about 5 to 30 seconds, in the subablation mode to increase the depth of thermal damage to the disc tissue.
In one method, high frequency voltage is applied, in the ablation mode, between one or more active electrode(s) and a return electrode spaced axially from the active electrode(s), and the active electrode(s) are advanced into the tissue to form a hole or channel as described above. High frequency voltage is then applied between the return electrode and one or more third electrode(s), in the thermal heating mode, as the electrosurgical instrument is removed from the hole. In one embodiment, the third electrode is a dispersive return pad on the external surface of the skin. In this embodiment, the thermal heating mode is a monopolar mode, in which current flows from the return electrode, through the patient""s body, to the return pad. In other embodiments, the third electrode(s) are located on the electrosurgical instrument and the thermal heating mode is bipolar. In all of the embodiments, the third electrode(s) are designed to increase the depth of current penetration in the tissue over the ablation mode so as to increase the thermal damage applied to the disc.
In another method, the third or coagulation electrode is placed in the thermal heating mode at the same time that the active electrode(s) is placed in the ablation mode. In this embodiment, electric current is passed from the coagulation electrode, through the tissue surrounding the hole, to the return electrode at the same time that current is passing between the active and return electrodes. In a specific configuration, this is accomplished by reducing the voltage applied to the coagulation electrode with a passive or active voltage reduction element coupled between the power supply and the coagulation electrode. In this manner, when the coagulation electrode is advanced into the tissue, the electric circuit between the coagulation and return electrodes is closed by the tissue surrounding the hole, and thus immediately begins to heat and coagulate this tissue.
In another method, an electrosurgical instrument having an electrode assembly is dipped into electrically conductive fluid such that the conductive fluid is located around and between both active and return electrodes in the electrode assembly. The instrument is then introduced into the patient""s spine either percutaneously or through an open procedure, and a plurality of holes are formed within the disc as described above. The instrument is removed from each hole in the thermal heating mode to create thermal damage and to coagulate blood vessels. Typically, the instrument will be dipped into the conductive fluid after being removed from each hole to ensure that sufficient conductive fluid exists for plasma formation and to conduct electric current between the active and return electrodes. This procedure reduces the volume of the intervertebraldisc, which helps to alleviate neck and back pain.
In another aspect of the invention, a method for treating a degenerative intervertebral disc involves positioning one or more active electrode(s) adjacent to selected nerves embedded in the walls of the disc, and positioning one or more return electrode(s) in the vicinity of the active electrode(s) in or on the disc. A sufficient high frequency voltage difference is applied between the active and return electrodes to denervate the selected nerves or to break down enzyme systems and pain generating neurotransmitters in the disc, and thus relieve pain. In some embodiments, the current path between the active and return electrode(s) is generated at least in part by an electrically conductive fluid introduced to the target site. In others, the disc tissue completes this current path.
In another aspect of the invention, a method for treating degenerative intervertebral discs involves positioning one or more active electrode(s) adjacent to or within the nucleus pulposis, and positioning one or more return electrode(s) in the vicinity of the active electrode(s) in or on the disc. A sufficient high frequency voltage difference is applied between the active and return electrodes to reduce water content of the nucleus pulposis and/or shrink the collagen fibers within the nucleus pulposis to tighten the disc. In some embodiments, the current path between the active and return electrode(s) is generated at least in part by an electrically conductive fluid introduced to the target site. In others, the disc tissue completes this current path.
In yet another aspect of the invention, a method for treating degenerative intervertebral discs involves positioning one or more active electrode(s) adjacent to or within a annular fissure on the inner wall of the annulus fibrosis, and positioning one or more return electrode(s) in the vicinity of the active electrode(s) in or around the disc. A sufficient high frequency voltage difference is applied between the active and return electrodes to weld, seal or shrink the collagen fibers in the annular fissure, thus repairing the fissure. Typically, the voltage is selected to provide sufficient energy to the fissure to raise the tissue temperature to at least about 50xc2x0 C. to 70xc2x0 C. for a sufficient time to cause the collagen fibers to shrink or weld together. In some embodiments, the current path between the active and return electrode(s) is generated at least in part by an electrically conductive fluid introduced to the target site. In others, the disc tissue completes this current path.
Systems according to the present invention generally include an electrosurgical instrument having a shaft with proximal and distal ends, an electrode assembly at the distal end and one or more connectors coupling the electrode assembly to a source of high frequency electrical energy. The instrument will comprise a probe or catheter shaft having a proximal end and a distal end which supports the electrode assembly. The probe or catheter may assume a wide variety of configurations, with the primary purpose being to introduce the electrode assembly to the patient""s spine (in an open or endoscopic procedure) and to permit the treating physician to manipulate the electrode assembly from a proximal end of the shaft. The electrode assembly includes one or more active electrode(s) configured for tissue ablation, a return electrode spaced from the active electrode(s) on the instrument shaft and a third, coagulation electrode spaced from the return electrode on the instrument shaft.
The system further includes a power source coupled to the electrodes on the instrument shaft for applying a high frequency voltage between the active and return electrodes, and between the coagulation and return electrodes, at the same time. In one embodiment, the system comprises a voltage reduction element coupled between the power source and the coagulation electrode to reduce the voltage applied to the coagulation electrode. The voltage reduction element will typically comprise a passive element, such as a capacitor, resistor, inductor or the like. In the representative embodiment, the power supply will apply a voltage of about 150 to 600 volts rms between the active and return electrodes, and the voltage reduction element will reduce this voltage to about 20 to 300 volts rms to the coagulation electrode. In this manner, the voltage delivered to the coagulation electrode is below the threshold for ablation of tissue, but high enough to coagulation and heat the tissue.
The active electrode(s) may comprise a single active electrode, or an electrode array, extending from an electrically insulating support member, typically made of an inorganic material such as ceramic, silicone or glass. The active electrode will usually have a smaller exposed surface area than the return and coagulation electrodes such that the current densities are much higher at the active electrode than at the other electrodes. Preferably, the return and coagulation electrodes have relatively large, smooth surfaces extending around the instrument shaft to reduce current densities, thereby minimizing damage to adjacent tissue.
The apparatus may further include a fluid delivery element for delivering electrically conducting fluid to the active electrode(s) and the target site. The fluid delivery element may be located on the instrument, e.g., a fluid lumen or tube, or it may be part of a separate instrument. Alternatively, an electrically conducting gel or spray, such as a saline electrolyte or other conductive gel, may be applied to the electrode assembly or the target site. In this embodiment, the apparatus may not have a fluid delivery element. In both embodiments, the electrically conducting fluid will preferably generate a current flow path between the active electrode(s) and the return electrode(s).